1. Field of the Invention
The present invention relates to an organic electroluminescent display apparatus comprising a plurality of organic electroluminescent devices and a method of fabricating the same.
2. Description of the Background Art
Organic electroluminescent display apparatuses (hereinafter abbreviated to organic EL display apparatuses) are expected to be promising as display apparatuses in place of liquid crystal display apparatuses currently in widespread use, and the development for practical utilization is under way. In particular, active matrix organic EL display apparatuses comprising Thin Film Transistors (TFTs) as switching devices in respective pixels are capable of having larger screens and higher definition because of holding display data in each pixel, and are considered to be the leading apparatuses among the next generation flat panel displays.
An organic EL display apparatus includes a plurality of organic electroluminescent devices (hereinafter abbreviated to organic EL devices), and each organic EL device constitutes a pixel. In each organic EL device, electrons and holes are injected to a light emitting layer from an electron injecting electrode and a hole injecting electrode, respectively, to be recombined at an interface between the light emitting layer and the hole transporting layer or inside the light emitting layer near the interface. This causes organic molecules to be in an excited-state, and fluorescence is produced when the organic molecules in the excited-state return to the ground-state.
In an organic EL display apparatus, a plurality of organic EL devices are formed in the form of a matrix. A color organic EL display apparatus comprises pixels composed of organic EL devices emitting red light (hereinafter referred to as R pixels), pixels composed of organic EL devices emitting green light (hereinafter referred to as G pixels), and pixels composed of organic EL devices emitting blue light (hereinafter referred to as B pixels).
A plurality of R pixels, a plurality of G pixels, and a plurality of B pixels are arranged along one direction and the other direction intersecting at right angles with each other. Here, one direction and the other direction are named “row direction” and “column direction”, respectively. In other words, a group of a plurality of R pixels, G pixels, and B pixels are periodically arranged along the row direction, and a plurality of R pixels, a plurality of G pixels, and a plurality of B pixels are arranged in the column direction, respectively.
Each organic EL device has a stacked structure in which a hole transporting layer, a light emitting layer, and an electron transporting layer are sequentially formed between a hole injecting electrode (anode) and an electron injecting electrode (cathode). The light emitting layers of R pixels, G pixels, and B pixels are composed of different materials.
In general, organic EL devices are formed by vacuum vapor deposition (see, for example, JP 2001-93667 A). In order to form an organic EL device in each pixel, a mask having apertures corresponding to respective pixels on the hole injecting electrodes on the substrate is provided so as to selectively deposit on the substrate the organic materials evaporated from vapor deposition sources corresponding to R pixels, G pixels, and B pixels.
However, deviation of the position of the mask may be caused in deposition of organic material layers using the mask having apertures corresponding to respective pixel. This deviation of the position of the mask may then lead to deviation of the positions of the organic material layers such as light emitting layers, consequently resulting in the narrowed effective light emitting area and the degradation of the yield of a product.
Furthermore, the thickness of the organic material layers may become ununiform due to the shadowing from end portions of the apertures of the mask. In this case, the thickness of the organic material layers, though almost uniform near the center portion, become smaller at the end portions of the apertures. This not only prevents the uniform light emitting properties, but causes the effective light emitting area to be reduced.